1. Field of the Invention
The present invention relates in general to a cylindrical damping device suitably used as a member mount for a suspension system of a motor vehicle, for example, and more particularly to a cylindrical fluid-filled damping device capable of exhibiting a damping effect with respect to a vibrational load received in its axial direction, on the basis of flows of a fluid therethrough.
2. Discussion of the Prior Art
As a damping device of a type adapted to be interposed between two members of a vibration system so as to elastically connect these two members, there is known a cylindrical damping device in which a center shaft member and an outer cylindrical member are disposed in a radially spaced-part relation with each other and are elastically connected to each other by an elastic body interposed therebetween. The cylindrical damping device is adapted to damp primarily a vibrational load applied thereto in its axial direction, namely, in the axial directions of the center shaft member and outer cylindrical member. Examples of this type of cylindrical damping device include a suspension member mount, a strut bar cushion and a suspension upper support for a motor vehicle.
Recently, there have been proposed cylindrical fluid-filled damping devices which are filled with a fluid and are adapted to damp input vibrations on the basis of flows or resonance of the fluid, with improved damping characteristics. An example of such a cylindrical fluid-filled damping device was developed by the assignee of this application and is disclosed in JP-U-62-158236 (laid-open publication of Japanese Utility Model Application), wherein a first and a second annular fluid chamber are formed in axially spaced-apart relation with each other, between a center shaft member and an outer cylindrical member. These first and second annular fluid chambers are filled with a non-compressible fluid and are held in communication with each other through an orifice passage.
The first and second annular fluid chambers are axially spaced apart from each other by a partition wall of the elastic body, and the axially outer ends of the fluid chambers are defined by axial end walls of the elastic body. The axially intermediate partition wall of the elastic body has a smaller radial height than the axial end walls. An orifice member is fixedly interposed between the outer circumferential surface of the partition wall and the outer cylindrical member, so that the orifice member cooperates with the outer cylindrical member to define the orifice passage. Upon application of an axial vibrational load to the damping device, the fluid pressures within the first and second annular fluid chambers are changed relative to each other due to different amounts of elastic deformation of the intermediate partition wall and the axial end walls of the elastic body, whereby the fluid is forced to flow through the orifice passage.
Generally, the cylindrical fluid-filled damping device is manufactured by: first forming the elastic body which is bonded by vulcanization to the outer circumferential surface of the center shaft member and which has a first and a second annular pocket on the opposite axial sides of the intermediate partition wall; fitting the orifice member on the outer circumferential surface of the intermediate partition wall; and finally mounting the outer cylindrical member on the outer circumferential surface of an intermediate product consisting of the center shaft member, elastic body and orifice member, while the intermediate product is submerged in a mass of the non-compressible fluid, so that a first and a second fluid chamber formed by the first and second annular pockets closed by the outer cylindrical member are filled with the non-compressible fluid.
In such a cylindrical fluid-filled damping device, metal rings are bonded to the outer circumferential surfaces of the intermediate partition wall and the two axial end walls of the elastic body during vulcanization of the elastic body, for the purpose of assuring fluid tightness between the annular fluid chambers and the outer cylindrical member, more specifically, fluid tightness between the outer circumferential surfaces of the axial end walls of the elastic body and the outer cylindrical member, and for the purpose of fluid-tightly attaching the orifice member to the outer circumferential surface of the partition wall of the elastic body.
To produce the fluid-filled damping device with the three metal rings incorporated therein as described above, these three metal rings must be set and positioned relative to the center shaft member, within a mold in which a rubber material is injected and vulcanized to form the elastic body. This procedure tends to be cumbersome and time-consuming in suitably setting the center shaft member and metal rings, and the mold tends to be complicated. Thus, the provision of the metal rings on the elastic body leads to reduced efficiency and increased cost of manufacture of the cylindrical fluid-filled damping device. In this respect, the construction of the known damping device is not satisfactory.